[PATCH v4 00/15] sched: introduce for_each_process_rculock and for_each_thread_rculock

[Ye Liu <ye.liu@linux.dev>]

From: Ye Liu <liuye@kylinos.cn>

Introduce for_each_process_rculock(), for_each_thread_rculock() and
for_each_process_thread_rculock() macros that combine the existing
iteration macros with scoped_guard(rcu), so that the RCU read lock
is automatically acquired before iteration and released when the
loop exits — including via break, goto, or return.

The rest of the series converts manual rcu_read_lock()/
rcu_read_unlock() and guard(rcu)() pairs across mm/, kernel/, fs/,
lib/ and security/ to use the new macros.

Suggested by Michal Hocko for the oom_kill path [2].

Signed-off-by: Ye Liu <liuye@kylinos.cn>

---
Changes since v3 [4]:
  - Fix patch 5 (cpu/hotplug): title and commit message incorrectly
    said "thread iterator" and "for_each_thread_rculock" while the
    code converts for_each_process() to for_each_process_rculock().

Note: Patches 4, 11, and 13 received automated reviews from sashiko-bot
in the v3 thread [4] that were verified as false positives:

  - Patch 4: claimed the folio lock is dropped before collect_procs(),
    leading to a NULL deref on folio->mapping; the lock is held in all
    call paths.
  - Patch 11: claimed mixing goto/scope-based cleanup in
    alloc_retstack_tasklist(); the goto free label handles memory
    cleanup, not lock management.
  - Patch 13: claimed mixing goto/scope-based cleanup in
    __set_oom_adj(); goto err_unlock manages oom_adj_mutex while
    scoped_guard(rcu) manages the RCU read lock — different resources.

Changes since v2 [3]:
  - Split the kernel/ patch into per-subsystem patches, as the
    combined patch could not be applied (Peter Zijlstra, Steven
    Rostedt).
  - Move changelog below the --- separator so it is excluded from
    the commit message (Lorenzo Stoakes).
  - Indent loop body in macro definitions to show scoped_guard
    scope (Lorenzo Stoakes).

Changes since v1 [1]:
  - Rename macros from *_rcu to *_rculock, as suggested by Steven
    Rostedt and acked by Thomas Gleixner, to avoid confusion with
    existing *_rcu() list iterators that expect the caller to hold
    the RCU read lock.
  - Improve the comment on for_each_process_thread_rculock() to
    document that 'break' only exits the inner loop and 'goto' is
    needed to exit both loops (Thomas Gleixner).
  - Rename the stale 'unlock:' label to 'out:' in hung_task.c, as
    noted by Günther Noack.
  - Clarify in patch 4 that page_pgoff() is safe outside the RCU
    read-side critical section (SJ Park).
  - CC all relevant maintainers on every patch (Lorenzo Stoakes).
  - Drop the mm: prefix from patch 1, as the macros are in
    include/linux/sched/signal.h (Michal Hocko).

[1] https://lore.kernel.org/all/20260904083001.553587-1-ye.liu@linux.dev/
[2] https://lore.kernel.org/all/20260813092933.562028-1-ye.liu@linux.dev/
[3] https://lore.kernel.org/all/20260907081334.1152889-1-ye.liu@linux.dev/
[4] https://lore.kernel.org/all/20260911075800.491472-1-ye.liu@linux.dev/

Ye Liu (15):
  sched: introduce for_each_process_rculock and for_each_thread_rculock
  mm/oom_kill: convert process/thread iterators to for_each_*_rculock
  mm/ksm: convert process iterator to for_each_process_rculock
  mm/memory-failure: convert process iterator to
    for_each_process_rculock
  cpu/hotplug: convert process iterator to for_each_process_rculock
  freezer: convert thread iterator to for_each_thread_rculock
  hung_task: convert process/thread iterators to for_each_*_rculock
  locking/lockdep: convert process/thread iterators to
    for_each_*_rculock
  rcu: convert process/thread iterator to
    for_each_process_thread_rculock
  sched: convert process/thread iterators to for_each_*_rculock
  tracing/fgraph: convert process/thread iterator to
    for_each_process_thread_rculock
  unwind: convert process/thread iterator to
    for_each_process_thread_rculock
  fs: convert process/thread iterators to for_each_*_rculock
  lib: convert process iterator to for_each_process_rculock
  security/landlock: convert thread iterator to for_each_thread_rculock

 fs/proc/base.c               |  4 +---
 fs/resctrl/rdtgroup.c        |  8 ++------
 include/linux/sched/signal.h | 26 ++++++++++++++++++++++++++
 kernel/cpu.c                 |  4 +---
 kernel/freezer.c             |  4 +---
 kernel/hung_task.c           | 11 ++++-------
 kernel/locking/lockdep.c     |  4 +---
 kernel/rcu/update.c          |  4 +---
 kernel/sched/core.c          |  3 +--
 kernel/sched/debug.c         |  4 +---
 kernel/trace/fgraph.c        |  8 ++------
 kernel/unwind/deferred.c     |  3 +--
 lib/is_single_threaded.c     |  5 +----
 mm/ksm.c                     |  4 +---
 mm/memory-failure.c          | 16 ++++------------
 mm/oom_kill.c                | 20 +++++---------------
 security/landlock/tsync.c    |  8 ++------
 17 files changed, 55 insertions(+), 81 deletions(-)

--
2.25.1